Answer: a = -3
Step-by-step explanation:
The point (3,a) means that x = 3 and y = a pair up together
Plug in those values and compute 'a'
y = 9-4x
a = 9-4(3)
a = 9-12
a = -3
The point (3, a) updates to (3, -3)
The point (3, -3) is on the line y = 9-4x